Easier way to check conditions?

I'm new to python and I need to simplify this checker. How can I change:

...
if c == '>' and ( prevTime > currentTime ):
    c2 = True
elif c == '>=' and ( prevTime >= currentTime ):
    c2 = True
...

to something like:

 if  prevTime | condition |  currentTime:
    doSomething()

I've tried to use either evaluate or compile, but during creation of string there is conversion between datetime object to string ( str on datetime开发者_Go百科 object). For example:

>>> 'result = %s %s %s' % (datetime.now(), '>', datetime.utcfromtimestamp(41))
'result = 2011-04-07 14:13:34.819317 > 1970-01-01 00:00:41'

and it can't be compared.

Can someone help me with this? Below working example:

def checkEvent( prevEvent, currentEvent, prevTime, currentTime ):

    def checkCondition( condition ):

        #condition format
        #tuple ( (oldEvent, newEvent), time, ip)
        # eg: (('co', 'co'), '>=', '!=')

        c1 = c2 = False

        #check Event
        if prevEvent == condition[0][0] and currentEvent == condition[0][1]:
            c1 = True
        else:
            return False

        #check time
        if condition[1]:
            c = condition[1]

            if c == '>' and ( prevTime > currentTime ):
                c2 = True
            elif c == '>=' and ( prevTime >= currentTime ):
                c2 = True
            elif c == '<' and ( prevTime < currentTime ):
                c2 = True
            elif c == '<=' and ( prevTime <= currentTime ):
                c2 = True
            elif c == '==' and ( prevTime == currentTime ):
                c2 = True

        else:
            c2 = True


        return c1 and c2


    def add():
        print 'add'

    def changeState():
        print 'changeState'

    def finish():
        print 'finish'

    def update():
        print 'update'    


    conditions = (\
                    ( ( ( 're', 'co' ), None ),  ( add, changeState ) ),
                    ( ( ( 'ex', 'co' ), None ),  ( add, changeState ) ),
                    ( ( ( 'co', 'co' ), '<'  ),  ( add, changeState ) ),
                    ( ( ( 'co', 'co' ), '>=' ),  ( add, changeState, finish ) ),
                    ( ( ( 'co', 'co' ), '>=' ),  ( update, ) ),
                    ( ( ( 'co', 're' ), '>=' ),  ( changeState, finish ) ),
                    ( ( ( 'co', 'ex' ), '>=' ),  ( changeState, finish ) ) 
                 )  


    for condition in conditions:
        if checkCondition( condition[0] ):
            for cmd in condition[1]:
                cmd()


from datetime import datetime

checkEvent( 'co', 'co', datetime.utcfromtimestamp(41), datetime.now() )
checkEvent( 'ex', 'co', datetime.utcfromtimestamp(41), datetime.now() )
checkEvent( 'co', 'co', datetime.utcfromtimestamp(41), datetime.utcfromtimestamp(40) )

You can try making a map of operators, like this:

import operator

compares = {
    '>': operator.gt,
    '>=': operator.ge,
    '<': operator.lt,
    '<=': operator.le,
    '==': operator.eq
}

def check(c, prev, current):
    func = compares[c]
    return func(prev, current)

print check('>', 5, 3)  # prints: True
print check('>=', 5, 5) # prints: True
print check('<', 3, 5)  # prints: True
print check('<=', 3, 3) # prints: True
print check('==', 7, 7) # prints: True

Folks do things like this:

result= { '=': lambda a, b: a == b,
    '>': lambda a, b: a > b,
    '>=': lambda a, b: a >= b,
    etc.
    }[condition]( prevTime, currentTime )

Are you looking for something like:

>>> eval('datetime.now() %s datetime.utcfromtimestamp(41)' % '>')
True

Your evals are failing because you're doing too much of the computation outside the eval.

Of course, the eval strategy itself is ugly; you should use one of the other answers ;)

You're only setting c1 = True if the function doesn't return, so it's guaranteed to be True at the end of the function. Factor it out.

The output of this function will be identical:

def checkEvent( prevEvent, currentEvent, prevTime, currentTime ):

    def checkCondition( condition ):

        #condition format
        #tuple ( (oldEvent, newEvent), time, ip)
        # eg: (('co', 'co'), '>=', '!=')

        #check Event
        if not (prevEvent == condition[0][0] and currentEvent == condition[0][1]):
            return False

        #check time
        c = condition[1]
        if not condition[1]:
            return True

        if c == '>' and ( prevTime > currentTime ):
            return True
        elif c == '>=' and ( prevTime >= currentTime ):
            return True
        elif c == '<' and ( prevTime < currentTime ):
            return True
        elif c == '<=' and ( prevTime <= currentTime ):
            return True
        elif c == '==' and ( prevTime == currentTime ):
            return True

        return False

Note: everyone else's "dict of functions" approach is the Pythonic way to do this. I just wanted to demonstrate a cleaned-up version of your original function that works in a way already familiar to you but with a more straightforward flow.